This invention relates to an improved fuel injection apparatus and, more particularly, to an improved fuel injection apparatus for uniformly atomizing and dispersing fuel supplied to a combustion chamber.
Fuel injection into a continuous flow combustion chamber, as, for example, in a gas turbine engine, has posed continuing design problems. Difficulties have been encountered in injecting fuel in a highly dispersed manner so as to achieve complete and efficient combustion of the fuel and at the same time minimize the occurrence of fuel rich pockets which, upon combustion, produce carbon or smoke. Fuel injection difficulties have been further complicated by the recent introduction of gas turbine engines having increased combustor pressure and inlet temperature capabilities requiring low pressure fuel devices. Existing fuel spray atomizer efficiency decreases as combustor pressure is increased, resulting in a more non-uniform dispersion of fuel, together with an increase in the fuel rich zones within the combustion chamber. Such zones cause reduced burner efficiency, excessive exhaust smoke, and a non-uniform heating of the combustor shell, a condition commonly referred to as hot streaking, which can lead to rapid deterioration of the shell.
Increasing the fuel pressure to spray atomizers has been suggested as one possible solution. However, the increased weight of a high pressure pump, together with the increased propensity of leaking the volatile high pressure fuel, imposes such a high risk as to make the use of high pressure pumps unlikely, at least within the immediate future.
Recently suggested atomizers for use with low pressure fuel have employed a system of counter-rotational primary and secondary swirl vanes. Some systems have suggested that a fuel/air mixture be introduced upstream of the swirl vanes, whereupon the fuel becomes uniformly dispersed by the action of the vanes. However, such atomizers have been found on occasion to accumulate carbon between the swirl vanes when the inlet airflow and fuel to the atomizer are heated. Present emphasis has centered on developing a system whereby a flow of fuel is introduced within a system of counter-rotational primary and secondary swirl vanes. The fuel is then efficiently atomized by the high shear forces developed at the confluence of the counter-rotating air streams.
Therefore, it is a primary object of this invention to provide a fuel injection apparatus that will uniformly disperse a low pressure fuel in a highly atomized manner into a combustion apparatus wherein the fuel is injected downstream of any air swirl vanes, thus eliminating the possiblity of carbon accumulation between the swirl vanes.
It is also an object of this invention to uniformly disperse fuel in a partially atomized manner for introduction into a counter-rotating swirl means to improve overall combustion efficiency thereof.
It is a further object of this invention to provide a fuel injection apparatus employing a system of counter-rotating swirl means disposed about a shroud member whereby the primary atomizing forces are the high shear stresses developed at the confluence of the counter-rotating air streams.
It is also an object of this invention to provide a fuel injection apparatus employing a system of counter-rotating swirl means disposed about a shroud member whereby the velocity and uniformity at which the fuel is dispersed within the shroud may be substantially modulated for greater overall atomization efficiency.